The proposed effort focuses on the final development of a high-frequency (100 MHz), broadband ultrasound microsystem designed to image cellular structure/tissue along the gastrointestinal (GI) tract. The unit fits within a standard GI endoscope. It consists of a paraboloid transmitter, a 16 x 16 ultrasound receiver array, a read-out integrated circuit (ROIC), and an interposer layer that links the latter two items. Fourteen-bit digitized data flow from the ROIC to an external computer where three-dimensional images are formed. The nominal sampled volume extends below the GI tract surface to depths in the range 1-3 mm, depending on the proximity of the sensor to the GI wall. The diameter of the probed volume ranges from 0.6 mm to 0.9 mm. The main functions of the imager include: 1) the imaging of pre-cancerous dysplastic mucosa, polyps, and adenomas, 2) real-time grading of dysplasia (pre-cancerous tissue), 3) immediate viewing of cellular structure in tumors (e.g., squamous cell carcinoma and adenocarcinoma, benign growths), 4) as required, guidance for directing fine-needle aspiration biopsies to regions that pose the greatest threat, and 5) the system serves as a patient friendly, pre-cancer diagnostic for severe gastroesophageal reflux disease (Barrett's esophagus). Overall, the suggested imager provides a new opportunity for the detection of pre-cancerous tissue along the GI tract, which at present is usually a chance finding and cannot be recognized endoscopically. The developmental prototype has a novel bistatic architecture aimed at increasing system sensitivity, reducing the time required to obtain an image, and simplifying the receiver system. A new sol-gel PZT (PbZr0.6Ti0.4O3) thick film, invented as part of the preceding NIH program, is used as the transducer material. It is much improved over previous efforts in this area. The PZT thick film density is 89-90% of the full thin film density and the thick film piezoelectric coefficients are very close to those of thin films. The advantage of the new thick film is 1) its patterning and fabrication process is well established and many methods are available, 2) it supports a very large etch selectivity of 15:1, 3) the fabrication/assembly process is straightforward and amenable to large-scale production, and 4) the fabrication process yields very inexpensive transducer arrays. The latter is very important because the transducer array/interposer/ROIC will be used only once and discarded. [unreadable] [unreadable] [unreadable]